Modern Buddy

Hi all...have had a pretty good week of riding with no issues since this last thread: viewtopic.php?t=16401&highlight=stall+choke

Previously, I had some stalling issues that seemed to be pointing to air mixture. But fiddling around with the idle screw only and replacing the sparkplug and boot got her running just fine.

However, last night coming home from dinner, I stalled going down a pretty significant hill. I was riding two up, had the scoot in third and was barely touching the throttle (~35-40 mph indicated). Definitely some engine breaking going on, and then sounded like she became air (or fuel) starved. Cut out near the bottom of the hill and couldn't get her back running. With the choke fully out was able to kick her and have her run for a few twists of the throttle and occasionally a few feet of movement. (then a 1/2 mile push uphill and a 1 mile coast while off downhill )

I think this is a vacuum issue...which is throwing off the air mixture. Some inspections this morning revealed that the air bellow between the air box and the frame is degraded. Odd part is that she ran perfectly for a week (with brief spurts at 40 mph). Could it be that the sustained speed going downhill last night "puffed" up the small splits in the bellow and made the issue more prominent? How would this impact not being able to start this morning?

If anyone could walk through (or point to existing thread) some vacuum tests (using carb cleaner/propane) it would be much appreciated.

Sounds like a seize. Do a compression test before running the motor much.

If the compression looks ok, the next thing I would look for is an engine air leak.

If one of the engine gaskets is leaking, that would cause the problems with stalling due to a lean mixture (the engine sucks in air from other places than the carb, and thus doesn't get fuel with it).

can you explain what a soft seize is? it's stock jetting, so i'm confused as to how it would happen.

also it would rev fine on the center stand...in neutral with the choke out. Could handle WOT, as well as put-put in idle for maybe 2-3 minutes at a time.

Stock jetting is VERY lean, especially at idle, to get passed EPA. It does sound like a soft seizure. Essentially the piston gets too hot from not enough fuel/oil mix and expands enough to score into the cylinder. You must remember that giving throttle not only lubricates the piston, but cools it as well. By using engine breaking with that much weight you created a lot of excess heat. The good thing is, if it is a soft seize you can overbore and fit an over-sized piston or kit the thing. Best to do a search over at stellaspeed.com, tuners are somewhat used to soft seizes.

the one thing that doesn't measure up is that i didn't have any wheel locking or anything like that...hence my asking what anachro meant by soft seize. i suppose it's possible (and can be checked with a compression test) but my two up weight was about 250 lbs (my friend and I are small people) and were, for the most part, cruising. perhaps i used engine breaking the wrong way...i'm just saying that I was considering popping up to 4th as i was starting to feel the limits of 3rd....it was still getting some fuel and oil.

also the fact that I had similar symptoms last week w/o a passenger and on level ground. it would often stall out as I let off the throttle in third gear in prep of slowing down for a traffic light or stop sign. and then take a couple days of fiddling to get running.

still sound like a seize to everyone?

will keep you all posted

the more reading, the more it sounds like seizing. again, will keep you posted.

To be honest engine breaking is a "no no" on 2T's. Although many have claimed to have done it for years, it is just bad ju ju, safer not to.

did some propane testing to see if i could find an air leak, but to no avail.

into the shop today...should have a report in a couple weeks. (yeah, our shop is a bit backed up!)

Back from the shop. Like me, they didn't find any evidence of air leaks...good news!

Carb into the ultrasonic cleaner seemed to do the trick. which is a good call, given that the previous owner let it sit for months. now just have to hope there isn't more gunk in the fuel tank

she runs like a champ now

JoshWED wrote:Back from the shop. Like me, they didn't find any evidence of air leaks...good news!

Carb into the ultrasonic cleaner seemed to do the trick. which is a good call, given that the previous owner let it sit for months. now just have to hope there isn't more gunk in the fuel tank

she runs like a champ now

Cool. I take it the bike compression tested out ok? Siezing due to running lean can get very expensive very quickly, so I'm glad it turned out well.

That said, if I thought my motor siezed, I would pull the head (its a simple job) and would inspect the cylinder walls. If they are torn up, I would stop running the bike and replace the piston and cylinder.

It is much better to err on caution, because if you get a hard sieze as a result of the existing damage, then you can destroy the entire motor rather than just the top end.

Not to mention eating pavement as your rear end locks up at speed.

Anachronism wrote: Cool. I take it the bike compression tested out ok? Siezing due to running lean can get very expensive very quickly, so I'm glad it turned out well.

That said, if I thought my motor siezed, I would pull the head (its a simple job) and would inspect the cylinder walls. If they are torn up, I would stop running the bike and replace the piston and cylinder.

It is much better to err on caution, because if you get a hard sieze as a result of the existing damage, then you can destroy the entire motor rather than just the top end.

@anach- My mechanic said compression was fine...it's my buddy's shop, so I trust said mechanic. Nevertheless, I finally got around to doing my own compression check gauge:

140 lbs

How's that for nicely broken in at 2600 miles! Squared.

Halloweenie wrote:Not to mention eating pavement as your rear end locks up at speed.

yes that sucks when you hard seize sucks big time thats why i have a choped front fender and olive has some of her battle scars